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Bobby Eshleman says: ==================== net: devmem: support devmem with netkit devices This series enables TCP devmem TX through netkit devices. Netkit now supports queue leasing. A physical NIC's RX queue can be leased to a netkit guest interface inside a container namespace. This gives the container a devmem-capable data path on the RX side (bind-rx, etc...). On the TX side, the container process binds to its netkit guest interface and sends traffic that netkit redirects (via BPF or ip forwarding) to the physical NIC for DMA. Two things in the existing devmem TX path prevent this from working: 1. validate_xmit_unreadable_skb() requires dev->netmem_tx before it will forward a dmabuf-backed (unreadable) skb. This protects skbs from landing on devices that don't have the IOMMU mappings for the backing dmabuf or that don't speak netmem. Netkit, however, does not support DMA, doesn't attempt to read unreadable skb pages and so doesn't break netmem (it is pure skb routing and redirection). It is functionally capable of routing unreadable skbs, but there is no way for the TX validation pathway to distinguish between a device that will actually attempt DMA-ing the skb and another device (like netkit) that does not DMA but also does not break netmem. 2. bind_tx_doit uses the bound device as the DMA device. When the user binds devmem TX to the netkit guest, the bind handler attempts to create DMA mappings against netkit, which has no DMA capability and no IOMMU mappings. This series solves these problems as follows: 1. Extend netmem_tx to two bits, assigned to one of three values: NETMEM_TX_NONE - netmem not supported NETMEM_TX_DMA - netmem supported and performs DMA NETMEM_TX_NO_DMA - netmem supported, but does not DMA With these bits, phys devices can set NETMEM_TX_DMA and devices like netkit set NETMEM_TX_NO_DMA. The validation TX path ensures that any DMA-capable netdev exactly matches the bound device, guaranteeing the correct mapping of the bound dmabuf. The validation TX path also allows devices with NETMEM_TX_NO_DMA to pass, knowing these devices will not misuse netmem or run into IOMMU faults. After redirection or routing and the skb finally makes its way through the stack to a physical device's TX path, the above NETMEM_TX_DMA check is performed again to guarantee the device has the appropriate binding/mappings. 2. On TX bind, the bind handler recognizes NETMEM_TX_NO_DMA devices and finds the phys TX device and binds to that instead. For the netkit case, if it has been leased a queue from a DMA-capable device already, then the bind action is performed on the DMA-capable device instead and the dmabuf is mapped correctly. ==================== Link: https://patch.msgid.link/20260514-tcp-dm-netkit-v5-0-408c59b91e66@meta.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. 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